Buffers ethyl acetate

Treatments Aqueous Buffer Ethyl Acetate Total Polar Metabolites... 

Laccase Oxidation of ferulic acid in sodium phosphate buffer/ethyl acetate to yield colorants [71]... 

Thermolysine Syntheses of N-(benzyloxycarbonyl)-L-alanyl-L-phenylalanine methyl ester and N-(benzyloxycarbonyl)-L-aspartyl-phenylalanine methyl ester in HEPES or MES-NaOH buffers/ethyl acetate [74]... 

Sample extraction/deproteinization is usually accomplished with mild acidic solvents to free the noncovalently bound tetracyclines from macromolecules. Mcllvaine buffer, pH 4.0 (286, 287), Mcllvaine/EDTA buffer, pH 4.0 (283, 287-293), succinate buffer, pH 4,0 (278-281,294-296), acidic acetonitrile (297-299), and acidic methanol (14, 199, 300) have all been used successfully. Moreover, trichloroacetic acid, pH 2.0 (301, 302), metaphosphoric acid (303), acetate buffer (126, 280), citrate buffer, pH 4.0 (304), citrate buffer/ethyl acetate, pH 4-5 (305), and hydrochloric acid/glycine buffer (306, 307) have all been employed with varying success to precipitate proteins from the sample homogenates. 

C2- ethyl Weak nonpolar Alkyl chains Buffers Ethyl acetate... 

Several enzymes can react with sterically hindered compounds. For example, the acetate of a tertiary alcohol can be hydrolyzed by papain in buffer-ethyl acetate (pH 6.5) with excellent -value (>400), affording the ( )-alcohol in 49% yield and 98% ee and the (S)-acetate in 50% yield and 99% ee. The remaining (S)-acetate was converted to 20(S)-camptothecin, which is a pentacyclic alkaloid with potent antitumor activity isolated from Camptotheca acuminata. The product ( )-acetate can be converted to the starting racemic acetate chemically in 70% yield (Fig. 10.22). 

Finally, attention was turned to neutral steroids, and as a representative model, cholic acid methyl ester 17 was chosen. The initial attempt to oxidize 17 in a biphasic aqueous buffer-ethyl acetate system, by the action of the usual NAD-dependent 7a-HSDH, was unsuccessful. To overcome this problem, a new 7a-HSDH, namely, the NADP-dependent 7a-HSDH from C. absonum [16], was considered. Unfortunately, the subsequent reduction of 65 occurred with a low degree of conversion (less than 20%), probably due to enzyme inactivation. The stability of 7p-HSDH was not improved by immobilization on solid supports such as Eupergit C or activated Sepharose [6]. 

Hydrogen peroxide has also been analy2ed by its chemiluminescent reaction with bis(2,4,6-trichlorophenyl) oxalate and perylene in a buffered (pH 4—10) aqueous ethyl acetate—methanol solution (284). Using a flow system, intensity was linear from the detection limit of 7 x 10 M to at least 10 M. 

Bj Pivaloyloxymethyl D(—)-Ot-aminobenzylpenicillinate. hydrochloride To a solution of pivaloyloxymethyl D(—)-a-azidobenzylpenicillinate (prepared as described above) in ethyl acetate (75 ml) a 0.2 M phosphate buffer (pH 2.2) (75 ml) and 10% palladium on carbon catalyst (4 g) were added, and the mixture was shaken in a hydrogen atmosphere for 2 hours at room temperature. The catalyst was filtered off, washed with ethyl acetate (25 ml) and phosphate buffer (25 ml), and the phases of the filtrate were separated. The aqueous phase was washed with ether, neutralized (pH 6.5 to 7.0) with aqueoussodium bicarbonate, and extracted with ethyl acetate (2 X 75 ml). To the combined extracts, water (75 ml) was added, and the pH adjusted to 25 with 1 N hydrochloric acid. The aqueous layer was separated, the organic phase extracted with water (25 ml), and the combined extracts were washed with ether, and freeze-dried. The desired compound was obtained as a colorless, amorphous powder. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Extraction and purification of luciferin and luciferase (Viviani etal., 2002a) To isolate luciferin, the lanterns of the Australian A. flava were homogenized in hot 0.1 M citrate buffer, pH 5, and the mixture was heated to 95°C for 5 min. The mixture was acidified to pH 2.5-3.0 with HCl, and luciferin was extracted with ethyl acetate. Upon thin-layer chromatography (ethanol-ethyl acetate-water, 5 3 2 or 3 5 2), the active fraction of luciferin was fluorescent in purple (emission Lav 415 nm when excited at 290 nm). To isolate the luciferase, the cold-water extract prepared according to Wood (1993 see above) was chromatographed on a column of Sephacryl S-300. On the same... 

Preparation of luciferase. Organisms were freeze-dried, powdered, and washed with ethyl acetate to destroy the majority of catalase activity. The washed residue was extracted with 50 mM potassium phosphate buffer, pH 6. The extract was fractionated by ammonium... 

Fig. 10.4.3 Left panel Bioluminescence spectrum of the acorn worm Ptychodera flava stimulated with H2O2. Right panel (a) The spectrum of the chemiluminescence emitted when 70% dioxane containing 1.7% H2C>2 (5 ml) was added to a mixture of a solution of 2,3,5,6-tetrabromohydroquinone (TBHQ) in ethyl acetate (2.5 ml), 50 mM glycine buffer (pH 12.0 2.5 ml), and riboflavin (b) when riboflavin was omitted and (c) when TBHQ was omitted. Dioxane was included to solubilize the ethyl acetate solution containing TBHQ. From Kanakubo et al., 2005, with permission from Elsevier.

Method B A solution of (/ )-oxynitrilase (150 pL, sec Method A) is dropped onto 2 g of Avicel cellulose [soaked in 20 mL of 0.01 M acetate buffer (pH 5.4) for 1 2 h, filtered off and pressed]. 20 mL of ethyl acetate (saturated with 0.01 M acetate buffer, pi I 5.4) are added, followed by 5 mmol of aldehyde and 250 pL (6.5 mmol) of hydrocyanic acid. After stirring at r.t. (Tabic 1) the mixture is filtered, and the filter cake pressed and washed with ethyl acetate. The combined solutions are dried and concentrated. 

Conjugate Addition. To a solution of 1.5 mmol of lithium dialkylcuprate at — 25 CC is added 1 mmol of methyl ( )-3-[(25,45,55)-3-benzyloxycarbonyl-4-methyl-5-phenyl-2-oxazolidinyl]-propenoate dissolved in 1 mL of dry diethyl ether. After 30 ntin at — 25 C, the mixture is treated with an aq NH3/NH4C1 pH 8 buffer solution and then stirred at r.t. for 15 min. After diethyl ether extraction, the organic layers are dried over Na,S()4 and filtered and the solvent is evaporated under reduced pressure. The crude products are checked by H- and l3C-NMR analyses in order to determine the diastereomer ratios (g 95 5) and then purified by flash chromatography (hexane/ethyl acetate 80 20) yield 70-72%. 

Nonvolatile Nitrosamines In Tobacco. A method which we developed several years ago for the analysis of tobacco-specific nitrosamines (TSNA 31) involves extraction of tobacco with buffered ascorbic acid TpH 4.5) followed by partition with ethyl acetate, chromatographic clean-up on silica gel, and analysis by HPLC-TEA (Figure 9). Results obtained with this method for a large spectrum of tobacco products (Table IV), strongly support the concept that the levels of nitrate and alkaloids, and especially the methods for curing and fermentation, determine the yields of TSNA in tobacco products. Recent and as yet preliminary data from snuff analyses indicate that aerobic bacteria play a role in the formation of TSNA during air curing and fermentation. 

To test the quality of some synthetic dyes according to standardized procedures, a screening is recommended based on TLC analysis on silica plates 60 F 254 using elutions with an ethyl acetate pyridine water 25 25 20 (v v v) mixture. To determine purity and secondary dyes (components or by-products of a dye that are not allowed to be present), successive TLC separations are recommended or, for more accurate answers, HPLC-DAD using RP-18 columns and eluents like acetonitrile and phosphate buffer."... 

Eluent components should be volatile. Solvents such as ethyl acetate, isopropyl ether, diethylketone, chloroform, dichloromethane, and toluene as modifiers and n-hexane as diluent are recommended for normal phase chromatography. For reversed-phase systems, methanol or acetonitrile are used as modifiers. Such components as acetic acid or buffers, as well as ion association reagents, should be avoided. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

If the analyte contains either an acidic or a basic functionality, adjusting the pH of the extraction solvent to make the analyte either ionic or nonionic may be advantageous. To make an analyte that contains an acidic or basic functionality nonionic for extraction into a nonpolar solvent, a small amount (5% or less) of an organic acid (such as acetic acid or trifluoroacetic acid) or organic base (triethylamine) along with methanol (about 10%) can be added to diethyl ether or ethyl acetate. Conversely, buffered solutions can be used to control the pH precisely in such a way as to control the charge on an analyte and thus improve its extraction efficiency into polar solvents. 

Bispyribac-sodium is recovered as the free acid, bispyribac, from plant material and soil by acetonitrile-water (4 1, v/v) solvent extraction. After filtration, the acetoni-tirile is evaporated under reduced pressure. The aqueous residue is dissolved in buffer solution (pH 7.4) and washed with ethyl acetate to separate the impurities from the extract. Then the solution is acidified and extracted with ethyl acetate. The ethyl acetate is evaporated. The residue is methylated with trimethylsilyldiazomethane. 

Silica gel mini column, Sep-Pak Plus Silica To set up, attach a Sep-Pak Plus Silica column to a vacuum manifold and rinse with 10 mL of ethyl acetate Empore Cig extraction disks (3M) To set up, attach Cig extraction disks to a two-piece Alter funnel and load 30 g of Filter Aid 400 on its surface. Wash the Alter with 20 mL of acetoniAile and 20 mL of 0.01 M acetate buffer (pH 4) in that order Filter Aid 400 (3M)... 

Transfer the residue prepared as in Section 6.1.1 into a 300-nL separatory funnel with 25 mL of phosphate buffer solution (0.1 M, pH 7.4). Add 10 mL of saturated aqueous sodium chloride and 50 mL of 0.5 M sodium hydrogen carbonate to the funnel and shake the funnel vigorously for 1 min. Add 70 mL of ethyl acetate to wash the aqueous layer to the funnel, shake, separate, and discard the ethyl acetate layer. Repeat this extraction procedure three times. Add 2 mL of phosphoric acid and 20 mL of an acetate buffer solution (0.1 M, pH 4) to the aqueous layer and extract the mixmre with 50 mL of ethyl acetate three times. Combine the extracts and filter into a 500-mL round-bottom flask through 60 g of anhydrous sodium sulfate supported by a plug of cotton wool in a funnel. Concentrate the filtrate to dryness under reduced pressure. 

Ethyl acetate, Pesticide Grade, J.T. Baker Hexane, Resi-Analyzed, J.T. Baker Hydrochloric acid (HCl, 36.5-38.0%), J.T. Baker Hydrion pH buffer, VWR (cat. No. 34175-220)... 

Enzyme-linked immunosorbent assay (ELISA). Li and Li developed an ELISA procedure for imidacloprid to determine its residues in coffee cherry and bean extracts. A 25-g amount of sample extracted with 300 mL of methanol and 1% sulfuric acid (3 1, v/v) for 3 min. An aliquot of the sample extract (0.5 mL) is mixed with 1 mL of water and a gentle stream of nitrogen is used to evaporate methanol. The solution is then extracted with 1 mL of ethyl acetate, the extract is reconstituted in 1 mL of PBST (phosphate-buffered saline containing 0.05% Tween 20) and competitive ELISA is performed to quantify imidacloprid in the extract. Eor methanol extracts of coffee cherries and beans fortified with imidacloprid at 0.5 mgL recoveries of imidacloprid by the ELISA method were 108 and 94, respectively. 

Ethyl acetate — OS-phosphate buffer pH 7 (2/1) 20 /S-Hydroxy steroid dehydrogenase... 

Example. A solution of ethyl acetate in pH 10.0 buffer (25°C) 1 hour after preparation was found to contain 3mg/mL. Two hours after preparation, the solution contained 2mg/mL. Calculate the... 

Example. A solution of ethyl acetate in pH 9.5 buffer (25°C) was assayed in triplicate several times over a 20-hour period. The data obtained are presented in Table 2. The results were plotted on semilogarthmic graph paper as shown in Fig. 3. Calculate the psuedo-first-order rate constant for the hydrolysis of ethyl acetate at pH 9.5 (25°Q. 

Purify the derivatized dendrimer using gel filtration (size exclusion chromatography) on a desalting column or through use of ultrafiltration spin-tubes (for G-4 and above). For smaller dendrimers, the derivatives may be purified by repeated precipitation from a meth-anolic solution by addition of ethyl acetate, dioxane, or benzene. The SPDP-dendrimer may be dried by lyophilization (if in water or buffer) or by solvent evaporation in vacuo (if the precipitation method was used). 

Alternatively, lipospheres might be prepared by a solvent technique. In this case, the active agent, the solid carrier, and the phospholipid are dissolved in an organic solvent such as acetone, ethyl acetate, ethanol, or dichloromethane. The solvent is then evaporated and the resulting solid mixed with warm buffer solution, and mixing is continued until a homogeneous dispersion of lipospheres is obtained. 

Samples are extracted into ethyl acetate from pH 9.0 buffer.. After evaporation of the solvent, n-triacontane, the internal standard, in pyridine/chloroform is added to the residue. 

Dobutaraine hydrochloride may be determined spectrophotometrically in 0.5 M hydrochloric acid at the maximum of 278 nm. If excipients interfere, the drug may be extracted into ethyl acetate from pH 9 buffer followed by extraction into 0.5 M hydrochloric acid for the UV measurement. 

FIGURE 1.23 Dependency of extraction recovery of ABT-869 and acid metabolite AB849529 on buffer pH and proportion of ethyl acetate in organic solvent.137 (Reproduced with permission from John Wiley Sons.)... 

To suppress the noncatalyzed reaction (which decreases the enantioselec-tivity) between acetone cyanohydrin and the substrate, ethyl acetate is required as a co-solvent, and a low reaction temperature is also essential. Han et al.22 found that in organic solution with a trace amount of water the above reaction proceeds with the same high enantioselectivity as in the presence of an aqueous buffer. The reaction can be carried out at a wide range of temperatures from 0° to 30° C. To avoid using highly toxic potassium or sodium cyanide, acetone cyanohydrin is used as a cyano donor. 

The crude material was purified by flash chromatography on silica gel (20 g) buffered with 1 % triethylamine, using petroleum ether ethyl acetate (9 1) as eluent to give the epoxide as a grey oil (104mg, 0.78 mmol, 78% yield). 

Mix 0.01 M dimethyltryptamine, 0.02 M phosphate buffer pH 7.2 containing 5 mM ascorbic acid, 0.02 M disodium EDTA and 0.01 M ferrous sulfate (CuCI may substitute) and add with stirring at 20-22° 0.02 M H202 (0.01 M may increase yield). Let reaction proceed to completion (2 hours or less) and extract with ethyl acetate. Dry and evaporate in vacuum to get about 30% yield of psilocin. The product, which contains the other OH-DMT s as well, can be chromatographed on silica thin layer with t-butanol-acetic acid-water (ACS 22,1210 (1968)) or on a 5% alumina-Nickel... 

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